Conventionally, a color scanner, as illustrated in FIG. 1, includes a light source 1 which illuminates an image 5 such that the light incident upon the image is reflected down upon a CCD sensor or full width array 3 (hereinafter "sensor"). To obtain the color information of the image, conventional color scanners utilize a variety of different methods to separate the colors of the image.
For example, as illustrated in FIG. 2, the sensor 3 may have particular color filters positioned on it. As shown in FIG. 2, the sensor 3 has a row of pixels 7 over which a red filter 9 is placed. Next to this row of pixels having a red filter placed thereon, a second row of pixels 7 have a green filter 9' placed over them. Lastly, a third row of pixels 7 are situated such that a blue filter 9" is positioned over them. In other words, a conventional color scanner may utilize a sensor 3 which has three separate areas designated on the sensor for sensing particular colors of the image being scanned.
Another example of a conventional color scanner is illustrated in FIG. 3. In this example, a sensor 11 does not have any color filters placed above the individual photosites or pixels 7. To provide the proper color separation for scanning the image, a color wheel 13 is placed in the optical path between the light source 1 and the sensor 11. This color wheel contains three separate filters; red, green, and blue; which are rotated through the optical path to provide the proper color separation. It is noted, that this color wheel can be placed along any portion of the optical path to provide the proper color separation.
Lastly, a third example of a conventional color scanner is illustrated in FIG. 4. In this conventional color scanner, the red filter 15, green filter 15', and blue filter 15" are slid in and out of the optical path between the light source 1 and sensor 11. By sliding the red, green and blue filters (15, 15', and 15", respectively), in and out of the optical path between the light source 1 and sensor 11, this conventional color scanner can provide the necessary color separations to properly scan the image.
For color scanners to properly convert the color image to electronic signals, the color scanners need to simulate the color response of the human eye. This is conventionally done by scanning the color image with three separate color filters, normally red, green, and blue, as discussed above. However, since the color filters of a conventional scanner do not exactly match the spectral response of the human eye, only an imperfect conversion from this scanner output to a colormetric response (human eye) can be obtained.
For accurate color representation, it is necessary to have a color scanner with a color response that matches the human eye. If a color scanner can accurately match the color response of the human eye, the color scanner can create an electronic file that completely describes the color of an object as seen by the human eye. Thus, the image could be potentially reproduced accurately by a printer or display.
As noted above, the spectral response of the human eye cannot be exactly matched with the filters in a typical color scanner. More specifically, the conventional color scanner, in an attempt to match the spectral response of the human eye, performs a color transformation to map the information received from the three color scans to the three color sensitivities defined by the human eye. Although the conventional scanner attempts to match the spectral response of the human eye through the utilization of a color transformation scheme, a universal match is usually not achieved utilizing the three conventional scans performed by the conventional scanner because of the physical limitations of the utilized color filters.
To achieve a more accurate match between the spectral response of the color scanner and the spectral response of the human eye, the present invention utilizes an additional filter or filters placed in the optical path between the light source and the CCD sensor or full width array so as to increase the number of color samples (scans). By increasing the number of color samples (scans) for a particular image, the color scanner can more accurately match the spectral response of the human eye.